DEVELOPMENT OF QUALITY CONTROL SYSTEM FOR DIAGNOSTIC X-RAY UNITS TO AIM REDUCTION OF PATIENT DOSE

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The purpose of this study is to measure diagnostic x-ray spectra using a high resolution Schottky CdTe detector (TOYO MEDIC RAMTEC 413A) and to determine the best response function of CdTe detector for correcting the measured spectra with using a rise time discrimination (RTD) circuit to primary x-ray spectra. Since the measured spectra were distorted by the response of CdTe detector and did not present the true photon spectra, the correction by the stripping procedure was applied. The response function of CdTe detector has been determined by using Monte Carlo simula-tion method for calculating the photon interaction (K-escape, coherent scattering and Compton scattering) and incomplete charge collection by trapping of hole and use of RTD circuit. This simulation performed with various important factors (mean path length. λ_h of hole and weight factor W_q of incomplete charge collection) for finding the best response function. The photon spectra corrected with those various response functions were compared with the corrected photon spectra measured using a high purity Ge (HP-Ge) detector (PRINCETON GAMMA-TECH NIGP1013345), and the Al-attenuation curves calculated from corrected spectra and measured using the HP-Ge detector were compared. The best-fitted response function was determined, and the attenuation curves calculated from the spectra corrected with this response function were agreed with that measured using the HP-Ge detector within maximum error 0.03 of the attenuation rate and 5.0 % of the half value layer.